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Subject[PATCH v2 2/2] mm: adds NOSIGBUS extension to mmap()
Date
Adds new flag MAP_NOSIGBUS of mmap() to specify the behavior of
"don't SIGBUS on fault". Right now, this flag is only allowed
for private mapping.

For MAP_NOSIGBUS mapping, map in the zero page on read fault
or fill a freshly allocated page with zeroes on write fault.

Signed-off-by: Ming Lin <mlin@kernel.org>
---
arch/parisc/include/uapi/asm/mman.h | 1 +
include/linux/mm.h | 2 ++
include/linux/mman.h | 1 +
include/uapi/asm-generic/mman-common.h | 1 +
mm/memory.c | 11 +++++++++++
mm/mmap.c | 4 ++++
tools/include/uapi/asm-generic/mman-common.h | 1 +
7 files changed, 21 insertions(+)

diff --git a/arch/parisc/include/uapi/asm/mman.h b/arch/parisc/include/uapi/asm/mman.h
index ab78cba..eecf9af 100644
--- a/arch/parisc/include/uapi/asm/mman.h
+++ b/arch/parisc/include/uapi/asm/mman.h
@@ -25,6 +25,7 @@
#define MAP_STACK 0x40000 /* give out an address that is best suited for process/thread stacks */
#define MAP_HUGETLB 0x80000 /* create a huge page mapping */
#define MAP_FIXED_NOREPLACE 0x100000 /* MAP_FIXED which doesn't unmap underlying mapping */
+#define MAP_NOSIGBUS 0x200000 /* do not SIGBUS on fault */
#define MAP_UNINITIALIZED 0 /* uninitialized anonymous mmap */

#define MS_SYNC 1 /* synchronous memory sync */
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 9e86ca1..100d122 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -373,6 +373,8 @@ int __add_to_page_cache_locked(struct page *page, struct address_space *mapping,
# define VM_UFFD_MINOR VM_NONE
#endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */

+#define VM_NOSIGBUS VM_FLAGS_BIT(38) /* Do not SIGBUS on fault */
+
/* Bits set in the VMA until the stack is in its final location */
#define VM_STACK_INCOMPLETE_SETUP (VM_RAND_READ | VM_SEQ_READ)

diff --git a/include/linux/mman.h b/include/linux/mman.h
index b2cbae9..c966b08 100644
--- a/include/linux/mman.h
+++ b/include/linux/mman.h
@@ -154,6 +154,7 @@ static inline bool arch_validate_flags(unsigned long flags)
_calc_vm_trans(flags, MAP_DENYWRITE, VM_DENYWRITE ) |
_calc_vm_trans(flags, MAP_LOCKED, VM_LOCKED ) |
_calc_vm_trans(flags, MAP_SYNC, VM_SYNC ) |
+ _calc_vm_trans(flags, MAP_NOSIGBUS, VM_NOSIGBUS ) |
arch_calc_vm_flag_bits(flags);
}

diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
index f94f65d..a2a5333 100644
--- a/include/uapi/asm-generic/mman-common.h
+++ b/include/uapi/asm-generic/mman-common.h
@@ -29,6 +29,7 @@
#define MAP_HUGETLB 0x040000 /* create a huge page mapping */
#define MAP_SYNC 0x080000 /* perform synchronous page faults for the mapping */
#define MAP_FIXED_NOREPLACE 0x100000 /* MAP_FIXED which doesn't unmap underlying mapping */
+#define MAP_NOSIGBUS 0x200000 /* do not SIGBUS on fault */

#define MAP_UNINITIALIZED 0x4000000 /* For anonymous mmap, memory could be
* uninitialized */
diff --git a/mm/memory.c b/mm/memory.c
index 8d5e583..6b5a897 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3676,6 +3676,17 @@ static vm_fault_t __do_fault(struct vm_fault *vmf)
}

ret = vma->vm_ops->fault(vmf);
+ if (unlikely(ret & VM_FAULT_SIGBUS) && (vma->vm_flags & VM_NOSIGBUS)) {
+ /*
+ * For MAP_NOSIGBUS mapping, map in the zero page on read fault
+ * or fill a freshly allocated page with zeroes on write fault
+ */
+ ret = do_anonymous_page(vmf);
+ if (!ret)
+ ret = VM_FAULT_NOPAGE;
+ return ret;
+ }
+
if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY |
VM_FAULT_DONE_COW)))
return ret;
diff --git a/mm/mmap.c b/mm/mmap.c
index 8bed547..d5c9fb5 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1419,6 +1419,10 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
if (!len)
return -EINVAL;

+ /* Restrict MAP_NOSIGBUS to MAP_PRIVATE mapping */
+ if ((flags & MAP_NOSIGBUS) && !(flags & MAP_PRIVATE))
+ return -EINVAL;
+
/*
* Does the application expect PROT_READ to imply PROT_EXEC?
*
diff --git a/tools/include/uapi/asm-generic/mman-common.h b/tools/include/uapi/asm-generic/mman-common.h
index f94f65d..a2a5333 100644
--- a/tools/include/uapi/asm-generic/mman-common.h
+++ b/tools/include/uapi/asm-generic/mman-common.h
@@ -29,6 +29,7 @@
#define MAP_HUGETLB 0x040000 /* create a huge page mapping */
#define MAP_SYNC 0x080000 /* perform synchronous page faults for the mapping */
#define MAP_FIXED_NOREPLACE 0x100000 /* MAP_FIXED which doesn't unmap underlying mapping */
+#define MAP_NOSIGBUS 0x200000 /* do not SIGBUS on fault */

#define MAP_UNINITIALIZED 0x4000000 /* For anonymous mmap, memory could be
* uninitialized */
--
1.8.3.1
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